The present invention relates to an apparatus for determining the effect of the configuration or topography of an outer surface on the drag of an object in a fluid and, in particular, to an apparatus and method used to determine the effect of surfaces having riblets and other small surface irregularities on the drag of an object in couette flow.
A reduction in the drag caused by the outer surface of an object can affect both the speed and direction of an object moving through a fluid. More specifically, the drag reducing effects of the outer surface of an object moving through a fluid, or the inner surface of an object through which a fluid moves, can be significant. Such drag reducing effects can have practical applications ranging from more efficient fluid flow in pipes to improving the performance of racing yachts.
A surface of parallel, elongated riblets has been shown to produce drag reductions in pipes and on flat plates, when the riblets meet certain specifications. It is desired to determine whether a riblet surface also reduces the drag of an object in couette flow, and to compare the results of different riblet profiler and other surface topographies.
To determine the extent to which riblet and other surfaces can reduce the drag of an object in couette flow, a method and testing apparatus is needed. The method and testing apparatus must enable the accurate comparison of the drag reduction of each surface tested.